1. Field of the Invention
The present invention relates to a switching regulator that is capable of reducing a rush current that flows at the time of starting.
2. Description of the Related Art
In general, a chopper type step-up switching regulator is mainly made up of, as shown in a circuit diagram of FIG. 4, an inductor 403, a rectifying device 404, a smoothing capacitor 405, a switching device 407 and a control circuit 406. In the switching regulator thus structured, even if the switching device 407 is turned off to stop the step-up operation, an energy is unavoidably supplied to a load device 402 from an input power supply 401 through the inductor 403 and the rectifying device 404.
Under the above circumstances, there has been conventionally known, as shown in FIG. 3, a switching regulator in which a switch 310 is disposed between an input power supply 301 and an inductor 303, a switch 311 is disposed between the inductor 303 and a switching device 307, a switch 312 is disposed between the switching device 307 and a rectifying device 304, a switch 313 is disposed between the rectifying device 304 and a smoothing capacitor 305, and a switch 314 is disposed between a smoothing capacitor 305 and a device 302, wherein those respective switches are turned off in order to interrupt the supply of an energy to the device 302 from the input power supply 301 when step-up operation stops.
However, in the conventional switching regulator, when the switch 310, the switch 311, the switch 312, the switch 313 or the switch 314 are turned on to start the step-up operation, a large rush current unavoidably flows into the smoothing capacitor 305 and a capacitor 309 added to the device from the input power supply 301 with an adverse effect that an input supply voltage drops or the rectifying device, the smoothing capacitor and so on are damaged by the rush current.
In view of the above, an object of the present invention is to solve the above problems with the conventional switching regulator.
Another object of the present invention is to provide a switching regulator which is capable of suppressing a rush current in which a switch for interrupting the supply of an energy to a device from an input power supply is not suddenly changed over from an inconductive state to a conductive state to permit a current to flow infinitely as soon as the switch turns on as in the conventional switching regulator, but a switch that limits a current or a switch that limits a current which flows for a given period of time, is employed.
In order to achieve the above objects, according to the present invention, there is provided a switching regulator, comprising:
an input power supply connected to an input of the switching regulator;
at least one input/output disconnection switch disposed between the input power supply and a device connected to an output of the switching regulator, for interrupting the supply of an energy to the device from the input power supply; and
means for limiting a rush current that flows into an output capacitor from the input power supply when the input/output disconnection switch turns on to start step-up operation.
Also, according to the present invention, in the switching regulator, the rush current limiting means of the input/output disconnection switch has a current limit function added to the output disconnection switch to set a limit value of a current that is allowed to flow.
Further, according to the present invention, in the switching regulator, the rush current limiting means of the input/output disconnection switch has a transistor as the output disconnection switch, the transistor operating in the same manner as that of an integral amplifying circuit to limit a current that flows for a given period of time.
Still further, according to the present invention, in the switching regulator, the rush current limiting means of the input/output disconnection switch repeats the on/off operation of the output disconnection switch to control an on-time and off-time, thereby limiting a current that is allowed to flow.